Recent advances in optical fiber technology have promoted the use of these light conducting elements as promising alternate media in the transmission of information signals. Typically, such fibers are light-transparent glass threads on the order of 0.01 inch or less in diameter encased in a sheath or cladding to which it is fused. Light enters at one end of the fiber and emerges from the opposite end with minimal loss. The physics of light transmission through a continuous fiber is now well-understood and need not be considered in detail for an understanding of the actuating mechanism of the invention. As in its electrical counterpart, the transmission of information signals in the form of light pulses for broad circuit applications requires some means for switching between one light transmission path and two or more other such paths. This has long been readily accomplished in the analogous transmission of electrical signals by providing electromechanical relay or switch means which are interposed in the circuits to be controlled. The electrical conductors of the circuits are simply soldered or otherwise connected to the relay or switch terminals. The switching of light transmission paths which include optical fibers has been accomplished more directly. Known optical fiber switching arrangements have generally contemplated the coupling of the actual light conducting media themselves without intervening contacting or circuit completion apparatus. Switching of light transmission paths thus presently involves the mechanical movement of the end of the actual conductive fiber itself out of alignment with the end of a second fiber and into alignment with the end of a third fiber. One such switching arrangement is disclosed in the copending application of W. C. Young, now U.S. Pat. No. 4,407,562, issued Oct. 4, 1983. As therein disclosed, two parallel rows of optical fibers are fixedly retained between silicon retaining blocks within an enclosing housing, the ends of the fibers lying in a common plane at the faces of the blocks. A third row of fibers, corresponding to the fibers in each of the two rows, is also retained between silicon retaining blocks, the ends of the fibers also lying in a common plane facing the ends of the first two rows of fibers. The blocks retaining the third row of fibers are movable within the housing to align the ends of the latter row with the corresponding ends of the fibers of either the first or second row of fibers. To accomplish this movement, a pair of opposing solenoids extending through the housing walls are contemplated which act upon opposite sides of the movable silicon block. Since the switching arrangement of the Young disclosure deals largely with the problem of positively retaining the optical fiber rows and maintaining their precise transverse and angular alignment during and after a switching operation, the actuating mechanism is referred to only to the extent of indicating that it comprises a pair of magnetically operated cores or solenoids acting directly upon the silicon retaining blocks.
A number of problems associated with the electromagnetic actuation of optical fiber switches generally are thus not addressed in the switching arrangement above briefly considered. The housing occupied by the fibers, for example, is filled with a suitable silicon type indexing fluid to minimize transmission losses between the fiber ends. To this end it is important that the transparency of the fluid be unaffected by contamination such as may result from chemical interactions with elements of incompatible materials also enclosed within the housing. Thus, if the number of active elements of the actuating mechanism within the housing is reduced to a minimum, the risk of fluid contamination is also reduced. The retention of the indexing fluid within the housing has in the past also presented a problem. This is especially the case where operating elements, such as the solenoids contemplated in the Young disclosure cited in the foregoing, movably extend through the housing walls. Adequate seals about the movable elements must be provided to prevent any fluid leakage. Such seals are costly and less than completely reliable over the long term. It is to these and other problems that the optical fiber switch actuating mechanism of the invention is chiefly directed.